This invention relates generally to the field of encapsulated components and to the manufacturing of such components. This invention relates more specifically to the field of electrical components that are encapsulated to improve their resistance to vibration and corrosive environments.
Encapsulation is a process by which a relatively fragile component is surrounded by an encasing material which provides mechanical support to the component and which may seal the component from contact with the ambient environment. Solid state electrical devices are known to be susceptible to printed circuit board failures due to vibration loads and/or mechanical or electrical degradation caused by exposure to a corrosive environment. The assignee of the present invention provides components for the marine environment wherein high levels of vibration and/or corrosive atmospheres may be commonplace. It is known to encapsulate such components to improve their performance in the marine environment. The encapsulant commonly used in such applications is an epoxy resin, selected for its workability, mechanical strength and electrical insulating properties. As commonly practiced, the encapsulant is poured in a fluid state into a case containing electrical devices, then allowed to cure to form a solid mass encasing the electrical devices within the case.
While the known process is effective to protect a component against vibration and environmental damage, failures may occur within the component due to mechanical damage caused by the thermal growth characteristics of the encapsulant. For example, it is known that such thermal growth may cause mechanical failure at the point where a conducting pin is soldered directly to a mating connector on a printed circuit board when the pin is fully constrained by being molded into a plastic case. Encapsulant disposed between the printed circuit board and the case is subject to thermal expansion and contraction. The thermal growth of the encapsulant may tend to move the printed circuit board away from the case. However, at the location of the soldered connection, the printed circuit board is maintained at a fixed distance from the case. The thermal expansion of the encapsulant may impose unacceptably high forces on the printed circuit board and/or the soldered connection. Encapsulated electrical components are known to have failed as the result of such differential thermal expansion.